Spectrally sensitized photoconductive recording material

ABSTRACT

Photoconductive zinc oxide for electrophotographic purposes is spectrally sensitized with methine dyes wherein the methine linkage connects two oxazole nuclei as such or forming part of a fused benzo-, naphto-, or furo-ring. The nuclei may be substituted with certain designated substituents. The photoconductive zinc oxide so sensitized is preferably applied from an aqueous coating medium to which the sensitizing agent was incorporated in the form of a solution thereof in an organic solvent which has a very low vapor pressure and is miscible with water in substantial proportions, a particularly preferred solvent being 4-hydroxy-4-methyl-2-pentanone.

United States Patent Inventors Appl. No.

Priority Karel Eugeen Verhille Mortsel;

Robert Joseph Noe, Mortsel; Lucinan Frans Voet, St. Katelijne-Waver; Henri De Poorter, Mortsel, all of Belgium 724,586

Apr. 26, 1968 Nov. 2, 1971 Gevaert-Agfa N.V.

Mortsel, Belgium Apr. 26, 1967 Great Britain SPECTRALLY SENSITIZED PHOTOCONDUCTIVE RECORDING MATERIAL 4 Claims, No Drawings [1.8. CI 96/l.7, 260/240 Int.Cl G03c 5/02, G03c 5/04 Field of Search 96/l .5, 1.7, I06; 260/240 M Grossweiner, Sensitization of Photoconductive Effects in Zinc Oxide," Photochemistry and Photobiology, Jan. 1968, Vol. 8,pp. 4| l-4l2 and4l6 Primary Examiner-George F. Lesmes Assistant Examiner-R. E. Martin At!0rney-William J. Daniel ABSTRACT: Photoconductive zinc oxide for electrophotographic purposes is spectrally sensitized with methine dyes wherein the methine linkage connects two oxazole nuclei as such or forming part of a fused benzo-, naphto-, or furo-ring. The nuclei may be substituted with certain designated substituents. The photoconductive zinc oxide so sensitized is preferably applied from an aqueous coating medium to which the sensitizing agent was incorporated in the form of a solution thereof in an organic solvent which has a very low vapor pressure and is miscible with water in substantial proportions, a particularly preferred solvent being 4-hydroxy-4-methyl-2- pentanone.

SPECTRALLY SENSITIZED PHOTOCONDUCTIVE RECORDING MATERIAL This invention relates to the spectral sensitization of photoconductive compositions, to such spectrally sensitized compositions, and to recording materials prepared therewith.

Photoconductive coatings containing a finely divided photoconductive substance e.g. photoconductive zinc oxide dispersed ina binder, are well known.

According to a technique disclosed in the U.S. Pat. Specification 3,l28,l79 photoconductive zinc oxide can be sensitized with various organic dyes, e.g., Rose Bengal. A particular class of sensitizing agents proposed in the latter U.S. Pat. Specification includes dyes known in the art as simple cyanine dyes, carbocyanine dyes, and dicarbocyanine dyes, provided such dyes contain at least one carboxy group.

Spectral sensitization of photoconductive zinc oxide coated on a support from a homogeneous dispersion in a solution of an insulating binder in water or in an organic solvent can be performedwith these dyesaln practice, however, their application is hindered considerably by their low fastness to light. Moreover, these dyes in general impart to the photoconductive layer a strong memory effect, in other words an irradiation of the layer before charging results in a prolonged state of conductivity of said layer. Preirradiation of a layer containing zinc oxide sensitized with these dyes considerably reduces the level to which the layer can be charged, unless the layer is stored for a sufficient time in the dark in order to regain its inherent chargeability.

Therefore, it is an object of the present invention to provide a class of spectral sensitizing agents for inorganic photoconductive substances such as photoconductive zinc oxide, which 7 are characterized by favorable spectral sensitizing effects in aqueous as well as in organic medium, and which possess in addition to fastness to light, the property of sensitizing the photoconductive substance in such a way that it acquires only a small memory effect.

Said object can be accomplished by the use of methine dyes corresponding to the following general formula:

Awherein: each of 0,, Q Q and 0,, represents hydrogen, alkyl including substituted alkyl, e.g. C,-C,, alkyl, aralkyl including substituted aralkyl e.g. benzyl, halogen, amino, substituted amino including said amino groups in salt or quaternary form, or Q, together with Q, and/or together with Q, represent the atoms necessary for closing a fused ring, e.g. a benzo-, naphto-, or furo-ring including such substituted ring, each of R, and R represents alkyl including substituted alkyl e.g. C,-C, alkyl, allyl, aralkyl, including substituted aralkyl e.g. benzyl, aryl including substituted aryl e.g. phenyl, at least one of R, and R representing sulfatoalkyl e.g. sulfatoalkyl as described in the French Pat. Specification 1,149,769, preferably sulfatoethyl, sulfatopropyl, sulfatobutyl and sulfatoisobutyl, or phosphonoalkyl wherein the alkyl group is preferably C,-C,, alkyl, such as described in the British Pat. Specification 886,270 or'a -A'(||3OBSO;OH

group wherein each ofA' and B represents alkylene or ylmethyl, w-sulfobutoxycarbonyl-methyl, or p-(w-sulfobutoxycarbonyl)-benzyl, or the groups -A-W-Nl-l-V-B or wherein each of W and V represents carbonyl, sulfonyl or a single bond, at least one of W or V being sulfonyl, A represents an alkylene group e.g. a C,-C, alkylene group and B represents hydrogen, alkyl including substituted alkyl, amino including substituted amino, e.g. acylamino, diethylamino, or dimethylamino, with the proviso, however, that B does not represent hydrogen when V represents carbonyl or sulfonyl as e.g. described in the British Pat. Specification 904,332 the groups -A-W-NH-V-B and being exemplified by N-(methylsulfonyl)-carbamyl-methyl, 'y- (acetyl-sulfamyl)-propyl, and 8-(acetylsulfamyl)-butyl, or a group wherein each of R and R, represents hydrogen, alkyl including substituted alkyl, amino including substituted amino and A" represents alkylene preferably C C, alkylene e.g. methylene, ethylene,propylene, or butylene, R represents hydrogen or alkyl including substituted alkyl e.g. C -C, alkyl or benzyl, X represents an anion, e.g., chloride, bromide, iodide, perchlorate, benzene sulfonate, toluene sulfonate, methyl sulfate, ethyl sulfate, propyl sulfate, but X is not present ifR, or R contains an anionic group, and n represents 1 or 2. I

The sensitizing dyes used in the present invention canbe allowed to absorb to the inorganic photoconductive substance, preferably photoconductive zinc oxide, by adding them to a dispersion of that substance in an organic or aqueous medium either or not already containing the binder.

Zinc oxiderecording layers applied from organic solvents and binding agents soluble in the organic medium are described e.g., in'the BelgianPat. Specification 612,102 and in the British-Pat. Application l9,l 86/67.

Zinc oxide recording layers applied from an aqueous medium are described e.g. in the published Dutch Pat. Applications 6608814 aiid6 6088l 5.

The spectral sensitizing agents are preferably added in dissolved state, e.g. dissolved in a water-miscible solvent or in water, to a dispersion of the photoconductive zincoxide. When appliediri an aqueous zinc oxide dispersion they are preferably incorporated into the recording layer from an organic liquid consisting of or containing a solvent, which has a weight soluble in water at 20 C. Such a method for sensitizing a photoconductive material is described in the published Dutch Pat. Application 6704768, which application should be read in conjunction herewith.

Suitable dispersing agents for dispersing photoconductive zinc oxide in an aqueous medium are described in the published Dutc'hPat. Application 6712156, which application should also be read in conjunction herewith.

When the sensitizing dyes of the present invention are used, the coloration of a recording layer containing white photoconductive zinc oxide can be kept very low for a very high sensitization yield.

The optimum quantity of sensitizing agent per gram of photoconductive zinc oxide can be determined easily by a series of tests. A useful range is comprised between 0.01 mg. and 1 mg. per gram of photoconductive zinc oxide. The weight ratio of zinc oxide to binder may vary between relatively large limits. A ratio of l part by weight of photoconductive substance to 0.1 to 0.6 part by weight of total content of binder is preferred. Advantageously, the coating mixture contains dispersed photoconductive zinc oxide in a weight ratio of percent to 60 percent in respect of the total solids content of the coated and dried layer. The thickness of the photoconduc- The present invention is further illustrated in the following example.

Example Preferably the sensitizing substances are used in combina- 5 tion with photoconductive zinc oxide prepared according to The following dispersions were prepared: the French process. Dispersion type A The photoconductive recording layers containing a spectral An amount of 1.972 kg. of a 20 percent solution of Vinsensitizing agent as above described may contain, in addition napas Bl00/20VL (a vinyl acetate polymer sold by Wacker to the photoconductive substance(s) and the binder, spectral l0 Chemie G.m.b.H. Munchen, West Germany) in ethylene sensitizing agents of any other type (see e.g. British Pat. chloride and asolution of48 g. of Hostalit CAM (aterpolymer Specification 1,020,504), compounds increasing the dark-reof vinyl chloride, vinyl acetate, and maleic anhydride, sold by sistivity, e.g. the phosphorus compounds described in the Farbwerke Hoechst, Frankfurt, West Germany) in a mixture Belgian Pat. Specification 612,102, and additives known in of 0.208 1. of ethanol and 0.4 l. of ethyl methyl ketone were coating techniques e.g. pigments (see e.g. British Pat. Specifiadded successively to 1.96 l. ofethylene chloride. cation 1,007,349), compounds influencing the gloss and/or The resulting solution was then diluted with 40 ml. of a 10 the viscosity, and compounds that counteract aging and/or oxpercent solution of tetrachloro-phthalic anhydride in ethanol idation 0f the layers, or which influence the thermal stability and 32 ml. of a 10 percent solution of acid butyl phosphate in of the layers. When selecting any additives, preference is given ethanol. Subsequently 1200 g. of photoconductive zinc oxide to those which least reduce the dark-resistivity of the (French Process) was added While stirring slowly. The disperphotoconductive layer sion was completed by mixing thoroughly in a sand-mill at a The photoconductive composition sensitized according to r f24 lJhour. the present invention may be coated on a support according to The dispersion was (muted at a rate of 62 8- 0f p a known coating technique, e.g., by s rayi hi li di 25 sion to 8 ml. of ethylenechlorrde and 1.2 rnl. of a 1 percent coating, or by a coating technique wherein use is made of a h h of the y (indicated table a Solvent doctor blade. The supports or base materials are chosen in heated table view of the particular charging, exposure, recording, develop- The dlspefstoh Y coated on a glasslhe yP P P P rata ment and/or transfer technique wherein the recording materiof 25 8- of Zinc Oxide P i q.m., dried, and stored in the dark a1 is 56 for 24 hours. The layer was then charged with a Corona of In electrophotographic recording techniques, wherein the 7000 f for 15 by Ofa E bulb photoconductive layer is electrostatically charged,the support wnh a radlano'? capacny of 2240 (2750 thmuh 8 preferably has an electric volume resistivity, which is cont wedge constant The number of enmcly siderably lower than that of the recording layer. Suitable supdlscharged areas (these of the recordmg s are ports are described e.g. in the British Pat. Specifications :f i z i 'j i gt a and cane? 995,491 and 1,020,504, 1,020,503 and in the us. Pat. 3. Steps F e as 3 S ecificafion 3 008 825. sitivrty of the layer.mcrease of that number by 3 means a p doubling of the sensitivity.

The photoconductive layer of an electrophotographrc Dispersion yp B "E which is prepared stanng q a coating 40 An amount of 20 g. of photoconductive zinc oxide, 25 cos. mfcordmg to l pre.sem tpvenuon can be used i of water, and 1 cc. ofa 10 percent solution of copoly(ma1eic recording purposies m .whlch to exposlne an electric anhydride/N-vinyl pyrrolidone) (5l.7/48.3) in aconcentrated cha'ge nondlfferenuauy ,apphed to known technical ammonia-water (1:9) solution was mixed for 10 f w the matenal can also be used m recordlng minutes with a high speed stirrer such as a Kothoff mixer. The techmquest m whlch t exposure step precedes the ,cllargmg dispersion was then added to a solution of 2 g. of poly(vinyl step. For such a technique we may refer to e.g. the British Pat. acetate/monk: acid) (944/16) and 125 of Cassum speclficauons 13031419 and 33 2 MLP (partially etherified melamine-formaldehyde resin mar- For compamon of the sensmmy of photoconducmfe kcted'as a 80 percent aqueous solution by Cassella Farbwerke, recording elements, said elements are charged and exposed in Mainkur AG" Frankfurt a/Main we Germany) in 25 of the Same manner, -B- through a P' E and developed in water and 1 cc. of a concentrated aqueous ammonia solution the same conditions. Well established methods of developing (25 percent by weight). The composition was sensitized by electrostatic images include Cascade" Powdet one of the sensitizing agents listed in the following table. Each netic brushand fur brush-development. These methods are sensitizing dye was added in an amount of0 5 per gram of based the application of charged y toner to the Surface zinc oxide in the form of a 0.1 percent solution and was intibearing the electrostatic image. Other methods are based on r i d i h h ground composiliom the use of liquids, either insulating (electrophoretic develop- E h iti d iti a oated o a baryta paper ment) or conductive liquids (see e.g. the U.S. Pat. Specificaweighing 90 g./sq.m. pro rata of25 g. ofzinc oxide per sq.m. tion 2,907,674 and the Belgian Pa Specifications 610.060 The layer was dried and stored in the dark for 24 hours. The n 5 Development Ofa conductivity image based charging, irradiation and development proceeded as described electrolysis is described e.g. by J. A. Amick, RCA Re 2 for Dispersion type A. The sensitometric results are also listed 753 (1959). MAW in table 1.

TABLE I Number of nonblackcned stops Solvent used Type A Type B for dissolving disperdisper- Dyc the dye sion sion 0 O Ethylene glycol 15 20 coH=oHoH=o monomcthyl other. ll l J 9 H zC N a) N- C H2- CH2CO-NHS02CH3 C Hs 4-hydrozy-4- 15 25 ccHoHcHc methyl-2- pentanonc.

Table 1- Continued Number of nonblackened Steps Solvent used Type A Type B for dissolving dlsperdisper- Dye the dye sion slon I n i C3111 Ethanol/water 16 (50 50 (\JCH=( J--CH=T x I Q l N l e l (CHmO S (CHZ)3OSO3H Dimethyl- 16 eoH=oH-c11=c formamlde. Q l CH2C 0-NHS O2CH3 CH2C O-NHS 02011:

We claim: 0- OR; 1. A photoconductive recording material comprising or photoconductlve layer applied from an aqueous coating comll R H position and containing zinc oxide in admixture with a spectral O 0 o sensitizing agent therefor corresponding to the general formula:

0 0 R represents hydrogen, benzyl or a C,-C, alkyl group, Q1 CH=(CCH)n-1= Qa X represents an anion, and l l l X n represent 1 or 2. Q N N Q4 2. A photoconductive recording material according to claim wherein:

each ofQ,, Q Q and Q represents hydrogen, a C -C alkyl group, a benzyl group, or Q together with 0 and/or 0;,

together with O represent the atoms necessary for closing a fused benzo, naphtho, or furon ring,

each of R and R, represents a -A-W-NH-V-B group, wherein each of W and V represents carbonyl, sulfonyl, or a monovalent chemical bond, at least one of W or V being sulfonyl, A represents a C -C alkylene group and B represents a lower alkyl group,

1, containing a photoconductive layer comprising photoconductive zinc oxide dispersed in a binder, which during the coating step was dissolved in an aqueous alkaline medium.

3. A photoconductive recording material comprising an inorganic photoconductive substance which is spectrally sensitized with a dye as described in claim 1. which dye in the formation of the photoconductive coating has been dissolved in an organic solvent having a very low vapor pressure and being miscible with water in concentrations of at least 20 percent by weight at 20 C.

4. A photoconductive recording material according to claim 3, wherein said solvent is 4-hydroxy-4-methyl-2-pentanone.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION November 2, 1971 3,617,269 Dated Patent No.

lnventofls) Karel Eugeen VERHILLE et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, Claim 1, line 25, delete the entirety of the formula beginning at A"-P etc.

Column 8, Claim 1, line 31, change "X to X Signed and sealed this 11th day of April 1972.

(SEAL) Attest:

ROBERT GOTTSCHALK EDWARD I I.FLETCHEJR,JR. Attesting Officer Commissioner of Patents USCOMM-DC GDS'FG-PGQ L) 5 GOVERNMENT PRINTING OFFICE 1 19.9 0-366-334 IIRM PO-IOSO (HI-69] 

2. A photoconductive recording material according to claim 1, containing a photoconductive layer comprising photoconductive zinc oxide dispersed in a binder, which during the coating step was dissolved in an aqueous alkaline medium.
 3. A photoconductive recording material comprising an inorganic photoconductive substance which is spectrally sensitized with a dye as described in claim 1, which dye in the formation of the photoconductive coating has been dissolved in an organic solvent having a very low vapor pressure and being miscible with water in concentrations of at least 20 percent by weight at 20* C.
 4. A photoconductive recording material according to claim 3, wherein said solvent is 4-hydroxy-4-methyl-2-pentanone. 